Until recently, measurement of BP required a mercury column and a skilled operator who was typically a trained nurse or doctor.
However, the advent of accurate automated electronic sphygmomanometers means that anyone with minimal training can now measure BP. Direct marketing of these devices to the public means that many patients are already measuring their BP at home.
Although there are no accurate figures available for the prevalence of self-monitoring of BP in the UK, it is known that many GPs and nurses are using self-monitoring for their patients.
In addition, BP measurement has penetrated the high street, with many pharmacies offering the service. Traditional weighing scales located in public areas such as airport lounges or railway station waiting rooms have been replaced in some cases by sophisticated electronic machines that record BP and other measurements, as well as weight.
One of the issues surrounding BP self-monitoring is whether it gives accurate readings and what the targets should be.
Studies show that BP measured in the waiting room gives a similar reading to that measured by a nurse but is slightly lower than that measured by a doctor - the average difference is around 5mmHg systolic.
Waiting room measurements are similar enough to those performed by nurses to use standard targets.
However, home readings are approximately 10/5mmHg lower than clinic readings and targets need to be adjusted downward by this amount. For example, standard NICE targets are 140/90mmHg for essential uncomplicated hyper-tension, which equates to a home reading of 130/85mmHg.
Evidence from randomised controlled trials suggests that self-measurement alone is enough to result in small reductions in BP. Two recent systematic reviews have found that BP can be reduced by 4/2mmHg by self-monitoring.
While this is perhaps not a huge impact for an individual, on a population basis this level of reduction would be expected to reduce the risk of stroke by around 10 per cent.
From a GP's perspective, it might have the additional beneficial effect of improving quality framework scores.
Most of the existing 20 or so randomised studies of self-monitoring originate from North America and Australia, but data are now available from a UK randomised trial of self-monitoring.
In a recent study, 441 people with poorly controlled treated hypertension drawn from eight general practices in the West Midlands were randomised between usual care - in terms of BP monitoring - and self-monitoring using shared electronic sphygmomanometers available in the practice waiting rooms.
All the trial participants received an information sheet regarding self-help measures to reduce BP, such as diet and exercise. Patients randomised to self-monitoring received about 10 minutes instruction on using the machines at baseline, with a five-minute refresher after six months.
The study showed that small reductions in BP of the order expected (4mmHg systolic) were achievable after six months, but after a year the reduction tailed off.
Importantly, the study showed those patients who self-monitored attended their GP and practice nurse less often - there was an approximate 20 per cent reduction in the consultation rate over a year.
This time saving meant that the costs of professional time for the initial training were cancelled out by the reduced consultation rate.
This, combined with the fact that machines were shared between a number of patients meant that overall costs were not significantly higher in the self-monitoring group.
The mechanism of action of BP reduction with self-monitoring seen in this study appears to be via non-pharmacological means. People who self-monitored were more likely to lose weight and reduce alcohol consumption than those who did not.
No difference in the rates of drug prescription or intensification of pharmacological treatment by GPs was detected. Presumably the feedback of BP results from self-monitoring increased the likelihood of an individual making non-pharmacological changes.
As well as being cost-effective, people with hypertension rate self-monitoring highly in comparison to professional monitoring. Most people in the trial discussed above managed to self-monitor for 12 months.
However, despite the evident cost-effectiveness of the method, monitors are still not available on the NHS and cost approximately £50 each. With almost six million people currently on hypertension registers in England alone, it appears likely that individuals will have to purchase their own machines.
One solution is for practices to purchase a small number of machines and share them using the model described above. However, before promoting self-monitoring in a practice, there are some key other issues to consider.
Validation and ease of use of the automated sphygmomanometer selected is very important. You can check validation via the BHS website or with your manufacturer.
Make sure you try before you buy and ask for a demonstration, particularly if you are choosing an expensive wall-mounted version.
You will need to train your staff to use the machines because they will be the ones who will train the patients.
This may be a nurse role in many practices but I have successfully trained receptionists to help patients and found them to have few problems.
Other practices have gone further and trained expert users to pass on their skills to other patients.
Calibration needs to be performed on a yearly basis, although some manufacturers claim it is not necessary for two years from initial purchase.
Consider teaming up with other practices to do this because it is much cheaper to have sphygmomanometers re-calibrated in bulk.
Privacy is an issue for waiting room measurements, particularly in small practices because some patients will not want to self-monitor in public.
You need to consider in advance what to do with the BP recordings that patients take and capture these for the practice computer system.
If patients are attending less frequently you will want feedback of their results, not least for the quality framework.
You will also need to consider establishing a protocol for what to do if the self-monitored BP reading is too high or too low.
- Dr McManus is clinical senior lecturer, department of primary care and general practice primary care, University of Birmingham
- Many people can now easily measure their BP. Increasingly, GPs and nurses are using self-monitoring for their patients.
- BP measured in the waiting room is around 5mmHg systolic lower than that measured by the doctor.
- Evidence from randomised controlled trials suggests that self-monitoring alone is enough to result in small reductions in BP.
- BP self-monitoring has been shown to be cost-effective. Those patients who self-monitored attended their GP or practice nurse less often.
- The GP will need to implement a protocol for capturing patients' self-monitored BPs and for what to do if the BP is too high or too low.